1. Chapter 17 – Files and Streams
Outline Introduction Data Hierarchy Files and Streams Classes File and Directory Creating a Sequential-Access File Reading Data from a Sequential-Access File Random-Access Files Creating a Random-Access File Writing Data Randomly to a Random-Access File Reading Data Sequentially from a Random-Access File Case Study: A Transaction-Processing Program

2. Variables and arrays only temporary
17.1 Introduction
Variables and arrays only temporary
Lost during garbage collection or when a program terminates
Files used for long term storage
Called persistent data
This chapter deals with:
Sequential-access files
Random-access files
File processing features
Stream-input/output features

3. 17.2 Data Hierarchy Data Hierarchy:
Gets more complex as you move along:
Bit: either one or zero
All data represented as combination of bits
Easy for electronic devices to understand
Byte: eight bits
Character: in C# two bytes
Character set: set of all characters used to program and represent data on a particular computer
Field: composition of characters that convey a meaning
Record: composition of several, related fields
File: group of related records
Record key: identifies record to a particular entity
Sequential file: records stored in order of record-key

4. 17.2 Data Hierarchy Randy Red Iris Orange Judy Green Tom Blue Sally
Black
file
record
Field
byte (ASCII for J)
bit
Fig Data hierarchy.

5. Files are sequential streams of bytes When file opened C#:
17.3 Files and Streams
Files are sequential streams of bytes
Ends with either an end-of-file marker or a specific byte
When file opened C#:
Creates an object
Associates a stream with that object
Three stream objects:
Console.In: returns standard input stream object
Console.Out: returns standard output stream object
Console.Error: returns standard error stream object
Namespace System.IO needed for file processing

6. BinaryFormatter: used to serialize and deserialize objects
17.3 Files and Streams
BinaryFormatter: used to serialize and deserialize objects
Serialize:converting an object into a format that can be written to a file without losing data
Deserialize: Reading formatted text from a file and reconstructing the original object from it
System.IO.Stream: allows representation of stream as bits
FileStream: read to and write from sequential-access and random-access files
MemoryStream:transfer of data directly to and from memory
BufferedStream: uses buffer to transfer to memory

7. 17.3 Files and Streams 1 2 3 4 5 6 7 8 9 n - 1 …… end of file marker
Fig C#’s view of an n-byte file.

8. 17.4 Classes File and Directory
Information stored in files
Files organized in directories
Directory class used to manipulate directories
File class used to manipulate files
Only has static methods, cannot instantiate File objects

9. 17.4 Classes File and Directory

10. 17.4 Classes File and Directory

11. Textbox for input of file or directory name
1 // Fig 17.5: FileTest.cs
2 // Using classes File and Directory. 3
4 using System;
5 using System.Drawing;
6 using System.Collections;
7 using System.ComponentModel;
8 using System.Windows.Forms;
9 using System.Data;
10 using System.IO; 11
12 // displays contents of files and directories
13 public class FileTestForm : System.Windows.Forms.Form
14 {
private System.Windows.Forms.Label directionsLabel; 16
private System.Windows.Forms.TextBox outputTextBox;
private System.Windows.Forms.TextBox inputTextBox; 19
private System.ComponentModel.Container components = null; 21
[STAThread]
static void Main() {
Application.Run( new FileTestForm() ); } 27
// Visual Studio .NET generated code 29
// invoked when user presses key
private void inputTextBox_KeyDown(
object sender, System.Windows.Forms.KeyEventArgs e ) {
FileTest.cs
Textbox for input of file or directory name
Event handler for keystrokes

12. Test if key typed was enter
// determine whether user pressed Enter key
if ( e.KeyCode == Keys.Enter ) {
string fileName; // name of file or directory 38
// get user-specified file or directory
fileName = inputTextBox.Text; 41
// determine whether fileName is a file
if ( File.Exists( fileName ) ) {
// get file's creation date,
// modification date, etc.
outputTextBox.Text = GetInformation( fileName ); 48
// display file contents through StreamReader
try {
// obtain reader and file contents
StreamReader stream = new StreamReader( fileName );
outputTextBox.Text += stream.ReadToEnd(); }
// handle exception if StreamReader is unavailable
catch( IOException ) {
MessageBox.Show( "File Error", "File Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); } } 63
// determine whether fileName is a directory
else if ( Directory.Exists( fileName ) ) {
// array for directories
string[] directoryList;
Test if key typed was enter
FileTest.cs
Set fileName to what user typed
See if fileName is an existing file
If an existing file, get and output file information
Create StreamReader to read text from file
Call method ReadToEnd
Test if fileName is existing directory

13. If it exists, get and output directory information FileTest.cs69
// get directory's creation date,
// modification date, etc.
outputTextBox.Text = GetInformation( fileName ); 73
// obtain file/directory list of specified directory
directoryList = Directory.GetDirectories( fileName ); 76
outputTextBox.Text +=
"\r\n\r\nDirectory contents:\r\n"; 79
// output directoryList contents
for ( int i = 0; i < directoryList.Length; i++ )
outputTextBox.Text += directoryList[ i ] + "\r\n"; }
else {
// notify user that neither file nor directory exists
MessageBox.Show( inputTextBox.Text +
" does not exist", "File Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); }
} // end if 92
} // end method inputTextBox_KeyDown 94
// get information on file or directory
private string GetInformation( string fileName ) {
// output that file or directory exists
string information = fileName + " exists\r\n\r\n";
100
// output when file or directory was created
information += "Created: " +
File.GetCreationTime( fileName ) + "\r\n";
If it exists, get and output directory information
FileTest.cs
Get subdirectories
Output subdirectories
If user input is not existing file or directory output error message
Tell user file exists
Get file creation information

14. Get last time file was modified
104
// output when file or directory was last modified
information += "Last modified: " +
File.GetLastWriteTime( fileName ) + "\r\n";
108
// output when file or directory was last accessed
information += "Last accessed: " +
File.GetLastAccessTime( fileName ) + "\r\n" + "\r\n";
112
return information;
114
} // end method GetInformation
116
117 } // end class FileTestForm
Get last time file was modified
FileTest.cs
Get last time file was accessed
Return file information

15. FileTest.cs Program Output

16. Used to store type and number of each file extension
1 // Fig 17.6: FileSearch.cs
2 // Using regular expressions to determine file types. 3
4 using System;
5 using System.Drawing;
6 using System.Collections;
7 using System.ComponentModel;
8 using System.Windows.Forms;
9 using System.Data;
10 using System.IO;
11 using System.Text.RegularExpressions;
12 using System.Collections.Specialized; 13
14 public class FileSearchForm : System.Windows.Forms.Form
15 {
private System.Windows.Forms.Label directionsLabel;
private System.Windows.Forms.Label directoryLabel; 18
private System.Windows.Forms.Button searchButton; 20
private System.Windows.Forms.TextBox outputTextBox;
private System.Windows.Forms.TextBox inputTextBox; 23
private System.ComponentModel.Container components = null; 25
string currentDirectory = Directory.GetCurrentDirectory();
string[] directoryList; // subdirectories
string[] fileArray; 29
// store extensions found and number found
NameValueCollection found = new NameValueCollection(); 32
FileSearch.cs
Used to store type and number of each file extension

17. Method to search recursively through directory path
[STAThread]
static void Main() {
Application.Run( new FileSearchForm() ); } 38
// Visual Studio .NET generated code 40
// invoked when user types in text box
private void inputTextBox_KeyDown(
object sender, System.Windows.Forms.KeyEventArgs e ) {
// determine whether user pressed Enter
if ( e.KeyCode == Keys.Enter )
searchButton_Click( sender, e ); 48
} // end method inputTextBox_KeyDown 50
// invoked when user clicks "Search Directory" button
private void searchButton_Click(
object sender, System.EventArgs e ) {
// check for user input; default is current directory
if ( inputTextBox.Text != "" ) {
// verify that user input is valid directory name
if ( Directory.Exists( inputTextBox.Text ) ) {
currentDirectory = inputTextBox.Text; 62
// reset input text box and update display
directoryLabel.Text = "Current Directory:" +
"\r\n" + currentDirectory; }
FileSearch.cs
Method to search recursively through directory path
Test if valid directory

18. If directory does not exist display error
else {
// show error if user does not specify valid directory
MessageBox.Show( "Invalid Directory", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); } } 74
// clear text boxes
inputTextBox.Clear();
outputTextBox.Clear(); 78
// search directory
SearchDirectory( currentDirectory ); 81
// summarize and print results
foreach ( string current in found ) {
outputTextBox.Text += "* Found " +
found[ current ] + " " + current + " files.\r\n"; } 88
// clear output for new search
found.Clear(); 91
} // end method searchButton_Click 93
// search directory using regular expression
private void SearchDirectory( string currentDirectory ) {
// search directory
try {
string fileName = "";
101
FileSearch.cs
If directory does not exist display error
If valid directory, call SearchDirectory
Display results of search

19. Define regularExpression as any file with extension FileSearch.cs
// regular expression for extensions matching pattern
Regex regularExpression = new Regex(
"[a-zA-Z0-9]+\\.(?<extension>\\w+)" );
105
// stores regular-expression-match result
Match matchResult;
108
string fileExtension; // holds file extensions
110
// number of files with given extension in directory
int extensionCount;
113
// get directories
directoryList =
Directory.GetDirectories( currentDirectory );
117
// get list of files in current directory
fileArray = Directory.GetFiles( currentDirectory );
120
// iterate through list of files
foreach ( string myFile in fileArray ) {
// remove directory path from file name
fileName = myFile.Substring(
myFile.LastIndexOf( "\\" ) + 1 );
127
// obtain result for regular-expression search
matchResult = regularExpression.Match( fileName );
130
// check for match
if ( matchResult.Success )
fileExtension =
matchResult.Result( "${extension}" );
Define regularExpression as any file with extension
FileSearch.cs
Get subdirectories
Get files of current directory
Search directory and subdirectory for bak files
Eliminate directory path to make comparison easier
Test if bak file
Store file extension

20. If not a match, store no extension
else
fileExtension = "[no extension]";
137
// store value from container
if ( found[ fileExtension ] == null )
found.Add( fileExtension, "1" );
else {
extensionCount = Int32.Parse(
found[ fileExtension ] ) + 1;
145
found[ fileExtension ] = extensionCount.ToString(); }
148
// search for backup(.bak) files
if ( fileExtension == "bak" ) {
// prompt user to delete (.bak) file
DialogResult result =
MessageBox.Show( "Found backup file " +
fileName + ". Delete?", "Delete Backup",
MessageBoxButtons.YesNo,
MessageBoxIcon.Question );
158
// delete file if user clicked 'yes'
if ( result == DialogResult.Yes ) {
File.Delete( myFile );
163
extensionCount =
Int32.Parse( found[ "bak" ] ) - 1;
166
If not a match, store no extension
FileSearch.cs
Test if first time extension was found
If first time, add extension to list
If not first time, increment extension counter
Test if bak file
Ask if user wants to delete bak file
If yes, delete file, decrement count

21. Search every subdirectory
found[ "bak" ] = extensionCount.ToString(); } } }
171
// recursive call to search files in subdirectory
foreach ( string myDirectory in directoryList )
SearchDirectory( myDirectory ); }
176
// handle exception if files have unauthorized access
catch( UnauthorizedAccessException ) {
MessageBox.Show( "Some files may not be visible" +
" due to permission settings", "Warning",
MessageBoxButtons.OK, MessageBoxIcon.Information ); }
184
} // end method SearchDirectory
186
187 } // end class FileSearchForm
FileSearch.cs
Search every subdirectory

22. FileSearch.cs Program Output

23. 17.5 Creating a Sequential-Access File
Programmers have to structure files to meet the requirements of applications

24. BankUI.cs Textboxes Labels 1 // Fig 17.7: BankUI.cs
2 // A reusable windows form for the examples in this chapter. 3
4 using System;
5 using System.Drawing;
6 using System.Collections;
7 using System.ComponentModel;
8 using System.Windows.Forms;
9 using System.Data; 10
11 public class BankUIForm : System.Windows.Forms.Form
12 {
private System.ComponentModel.Container components = null; 14
public System.Windows.Forms.Label accountLabel;
public System.Windows.Forms.TextBox accountTextBox; 17
public System.Windows.Forms.Label firstNameLabel;
public System.Windows.Forms.TextBox firstNameTextBox; 20
public System.Windows.Forms.Label lastNameLabel;
public System.Windows.Forms.TextBox lastNameTextBox; 23
public System.Windows.Forms.Label balanceLabel;
public System.Windows.Forms.TextBox balanceTextBox; 26
// number of TextBoxes on Form'
protected int TextBoxCount = 4; 29
BankUI.cs
Labels
Textboxes

25. Method to clear textboxes
// enumeration constants specify TextBox indices
public enum TextBoxIndices {
ACCOUNT,
FIRST,
LAST,
BALANCE 37
} // end enum 39
[STAThread]
static void Main() {
Application.Run( new BankUIForm() ); } 45
// Visual Studio .NET generated code 47
// clear all TextBoxes
public void ClearTextBoxes() {
// iterate through every Control on form
for ( int i = 0; i < Controls.Count; i++ ) {
Control myControl = Controls[ i ]; // get control 55
// determine whether Control is TextBox
if ( myControl is TextBox ) {
// clear Text property (set to empty strng)
myControl.Text = ""; } } 63
} // end method ClearTextBoxes
BankUI.cs
Method to clear textboxes

26. Method to set values of textboxes65
// set text box values to string array values
public void SetTextBoxValues( string[] values ) {
// determine whether string array has correct length
if ( values.Length != TextBoxCount ) {
// throw exception if not correct length
throw( new ArgumentException( "There must be " +
(TextBoxCount + 1) + " strings in the array" ) ); } 76
// set array values if array has correct length
else {
// set array values to text box values
accountTextBox.Text =
values[ ( int )TextBoxIndices.ACCOUNT ];
firstNameTextBox.Text =
values[ ( int )TextBoxIndices.FIRST ];
lastNameTextBox.Text =
values[ ( int )TextBoxIndices.LAST ];
balanceTextBox.Text =
values[ ( int )TextBoxIndices.BALANCE ]; } 90
} // end method SetTextBoxValues 92
// return text box values as string array
public string[] GetTextBoxValues() {
string[] values = new string[ TextBoxCount ]; 97
Method to set values of textboxes
BankUI.cs
Method to get the values of textboxes

27. BankUI.cs Program Output
// copy text box fields to string array
values[ ( int )TextBoxIndices.ACCOUNT ] =
accountTextBox.Text;
values[ ( int )TextBoxIndices.FIRST ] =
firstNameTextBox.Text;
values[ ( int )TextBoxIndices.LAST ] =
lastNameTextBox.Text;
values[ ( int )TextBoxIndices.BALANCE ] =
balanceTextBox.Text;
107
return values;
109
} // end method GetTextBoxValues
111
112 } // end class BankUIForm
BankUI.cs Program Output

28. Set members to parameters
1 // Fig. 17.8: Record.cs
2 // Serializable class that represents a data record. 3
4 using System; 5
6 [Serializable]
7 public class Record
8 {
private int account;
private string firstName;
private string lastName;
private double balance; 13
// default constructor sets members to default values
public Record() : this( 0, "", "", 0.0 ) { } 18
// overloaded constructor sets members to parameter values
public Record( int accountValue, string firstNameValue,
string lastNameValue, double balanceValue ) {
Account = accountValue;
FirstName = firstNameValue;
LastName = lastNameValue;
Balance = balanceValue; 27
} // end constructor 29
Record.cs
Tells compiler objects of class Record can be represented as a set of bits
Data to go into record
Sets members to 0
Set members to parameters

29. Record.cs Accessor methods 30 // property Account
public int Account {
get {
return account; } 37
set {
account = value; } 42
} // end property Account 44
// property FirstName
public string FirstName {
get {
return firstName; } 52
set {
firstName = value; } 57
} // end property FirstName 59
Accessor methods
Record.cs

30. Record.cs Accessor methods 60 // property LastName
public string LastName {
get {
return lastName; } 67
set {
lastName = value; } 72
} // end property LastName 74
// property Balance
public double Balance {
get {
return balance; } 82
set {
balance = value; } 87
} // end property Balance 89
90 } // end class Record
Accessor methods
Record.cs

31. 1 // Fig 17.9: CreateSequentialAccessFile.cs
2 // Creating a sequential-access file. 3
4 // C# namespaces
5 using System;
6 using System.Drawing;
7 using System.Collections;
8 using System.ComponentModel;
9 using System.Windows.Forms;
10 using System.Data;
11 using System.IO;
12 using System.Runtime.Serialization.Formatters.Binary;
13 using System.Runtime.Serialization; 14
15 // Deitel namespace
16 using BankLibrary; 17
18 public class CreateFileForm : BankUIForm
19 {
private System.Windows.Forms.Button saveButton;
private System.Windows.Forms.Button enterButton;
private System.Windows.Forms.Button exitButton; 23
private System.ComponentModel.Container components = null; 25
// serializes Record in binary format
private BinaryFormatter formatter = new BinaryFormatter(); 28
// stream through which serializable data is written to file
private FileStream output; 31
CreateSequentialAccessFile.cs

32. Instantiate SaveFileDialog object
[STAThread]
static void Main() {
Application.Run( new CreateFileForm() ); } 37
// Visual Studio .NET generated code 39
// invoked when user clicks Save button
private void saveButton_Click(
object sender, System.EventArgs e ) {
// create dialog box enabling user to save file
SaveFileDialog fileChooser = new SaveFileDialog();
DialogResult result = fileChooser.ShowDialog();
string fileName; // name of file to save data 48
// allow user to create file
fileChooser.CheckFileExists = false; 51
// exit event handler if user clicked "Cancel"
if ( result == DialogResult.Cancel )
return; 55
// get specified file name
fileName = fileChooser.FileName; 58
// show error if user specified invalid file
if ( fileName == "" || fileName == null )
MessageBox.Show( "Invalid File Name", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
CreateSequentialAccessFile.cs
Instantiate SaveFileDialog object
Show SaveFileDialog
Test if user canceled save
Get file name to save to

33. Instantiate output stream with write permission
else {
// save file via FileStream if user specified valid file
try {
// open file with write access
output = new FileStream( fileName,
FileMode.OpenOrCreate, FileAccess.Write ); 71
// disable Save button and enable Enter button
saveButton.Enabled = false;
enterButton.Enabled = true; } 76
// handle exception if file does not exist
catch ( FileNotFoundException ) {
// notify user if file does not exist
MessageBox.Show( "File Does Not Exist", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); } }
} // end method saveButton_Click 86
// invoke when user clicks Enter button
private void enterButton_Click(
object sender, System.EventArgs e ) {
// store TextBox values string array
string[] values = GetTextBoxValues(); 93
// Record containing TextBox values to serialize
Record record = new Record(); 96
CreateSequentialAccessFile.cs
Instantiate output stream with write permission
Method to save data when user clicks enter

34. Store TextBox fields in record
// determine whether TextBox account field is empty
if ( values[ ( int )TextBoxIndices.ACCOUNT ] != "" ) {
// store TextBox values in Record and serialize Record
try {
// get account number value from TextBox
int accountNumber = Int32.Parse(
values[ ( int )TextBoxIndices.ACCOUNT ] );
106
// determine whether accountNumber is valid
if ( accountNumber > 0 ) {
// store TextBox fields in Record
record.Account = accountNumber;
record.FirstName =
values[ ( int )TextBoxIndices.FIRST ];
record.LastName =
values[ ( int )TextBoxIndices.LAST ];
record.Balance = Double.Parse( values[
( int )TextBoxIndices.BALANCE ] );
118
// write Record to FileStream (serialize object)
formatter.Serialize( output, record ); }
else {
// notify user if invalid account number
MessageBox.Show( "Invalid Account Number", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); } }
129
CreateSequentialAccessFile.cs
Store TextBox fields in record
Write data to file

35. Catch block if user input invalid data
// notify user if error occurs in serialization
catch( SerializationException ) {
MessageBox.Show( "Error Writing to File", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); }
136
// notify user if error occurs regarding parameter format
catch( FormatException ) {
MessageBox.Show( "Invalid Format", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); } }
144
ClearTextBoxes(); // clear TextBox values
146
} // end method enterButton_Click
148
// invoked when user clicks Exit button
private void exitButton_Click(
object sender, System.EventArgs e ) {
// determine whether file exists
if ( output != null ) {
// close file
try {
output.Close(); }
161
CreateSequentialAccessFile.cs
Catch block if user input invalid data
Close FileStream

36. CreateSequentialAccessFile.cs Program Output
// notify user of error closing file
catch( IOException ) {
MessageBox.Show( "Cannot close file", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); } }
169
Application.Exit();
171
} // end method exitButton_Click
173
174 } // end class CreateFileForm
CreateSequentialAccessFile.cs Program Output
Exit program
BankUI graphical user interface

37. CreateSequentialAccessFile.cs Program Output
SaveFileDialogue
Files and directories

38. CreateSequentialAccessFile.cs Program Output

39. CreateSequentialAccessFile.cs Program Output

40. CreateSequentialAccessFile.cs Program Output

41. 17.5 Creating a Sequential-Access File

42. 17.6 Reading Data from a Sequential-Access File
Read data sequentially from a file
Programs usually start at beginning of file and read data consecutively until the desired data is found
Sometimes necessary to do this several times during execution of a program
File-position pointer:
Points to next byte to be read from or written to file
Can be repositioned to any point in file
RichTextBox:
LoadFile: method to display file contents
Find: method for searching individual strings
Can display multiple lines of text

43. 1 // Fig. 17.11: ReadSequentialAccessFile.cs
2 // Reading a sequential-access file. 3
4 // C# namespaces
5 using System;
6 using System.Drawing;
7 using System.Collections;
8 using System.ComponentModel;
9 using System.Windows.Forms;
10 using System.Data;
11 using System.IO;
12 using System.Runtime.Serialization.Formatters.Binary;
13 using System.Runtime.Serialization; 14
15 // Deitel namespaces
16 using BankLibrary; 17
18 public class ReadSequentialAccessFileForm : BankUIForm
19 {
System.Windows.Forms.Button openButton;
System.Windows.Forms.Button nextButton; 22
private System.ComponentModel.Container components = null; 24
// stream through which serializable data are read from file
private FileStream input; 27
// object for deserializing Record in binary format
private BinaryFormatter reader = new BinaryFormatter(); 30
[STAThread]
static void Main() {
Application.Run( new ReadSequentialAccessFileForm() ); }
ReadSequentialAccessFile.cs

44. Instantiate OpenFilelDialog36
// Visual Studio .NET generated code 38
// invoked when user clicks Open button
private void openButton_Click(
object sender, System.EventArgs e ) {
// create dialog box enabling user to open file
OpenFileDialog fileChooser = new OpenFileDialog();
DialogResult result = fileChooser.ShowDialog();
string fileName; // name of file containing data 47
// exit event handler if user clicked Cancel
if ( result == DialogResult.Cancel )
return; 51
// get specified file name
fileName = fileChooser.FileName;
ClearTextBoxes(); 55
// show error if user specified invalid file
if ( fileName == "" || fileName == null )
MessageBox.Show( "Invalid File Name", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
else {
// create FileStream to obtain read access to file
input = new FileStream( fileName, FileMode.Open,
FileAccess.Read ); 65
// enable next record button
nextButton.Enabled = true; } 69
} // end method openButton_Click
ReadSequentialAccessFile.cs
Instantiate OpenFilelDialog
Display OpenFileDialog
Create FileStream object for input with read only perimission

45. Method to view next record71
// invoked when user clicks Next button
private void nextButton_Click(
object sender, System.EventArgs e ) {
// deserialize Record and store data in TextBoxes
try {
// get next Record available in file
Record record =
( Record )reader.Deserialize( input ); 82
// store Record values in temporary string array
string[] values = new string[] {
record.Account.ToString(),
record.FirstName.ToString(),
record.LastName.ToString(),
record.Balance.ToString() }; 89
// copy string array values to TextBox values
SetTextBoxValues( values ); } 93
// handle exception when no Records in file
catch( SerializationException ) {\
// close FileStream if no Records in file
input.Close(); 99
// enable Open Record button
openButton.Enabled = true;
102
// disable Next Record button
nextButton.Enabled = false;
105
Method to view next record
ReadSequentialAccessFile.cs
Deserialize and cast next record
Display Record in TextBoxes
Exception thrown when there are no more records
Close FileStream

46. ReadSequentialAccessFile.cs Program Output
ClearTextBoxes();
107
// notify user if no Records in file
MessageBox.Show( "No more records in file", "",
MessageBoxButtons.OK, MessageBoxIcon.Information ); }
112
} // end method nextButton_Click
114
115 } // end class ReadSequentialAccessFileForm
ReadSequentialAccessFile.cs Program Output
Tell user there are no more records

47. ReadSequentialAccessFile.cs Program Output

48. ReadSequentialAccessFile.cs Program Output

49. ReadSequentialAccessFile.cs Program Output

50. ReadSequentialAccessFile.cs Program Output

51. CreditInquiry.cs 1 // Fig. 17.12: CreditInquiry.cs
2 // Read a file sequentially and display contents based on
3 // account type specified by user (credit, debit or zero balances). 4
5 // C# namespaces
6 using System;
7 using System.Drawing;
8 using System.Collections;
9 using System.ComponentModel;
10 using System.Windows.Forms;
11 using System.Data;
12 using System.IO;
13 using System.Runtime.Serialization.Formatters.Binary;
14 using System.Runtime.Serialization; 15
16 // Deitel namespaces
17 using BankLibrary; 18
19 public class CreditInquiryForm : System.Windows.Forms.Form
20 {
private System.Windows.Forms.RichTextBox displayTextBox; 22
private System.Windows.Forms.Button doneButton;
private System.Windows.Forms.Button zeroButton;
private System.Windows.Forms.Button debitButton;
private System.Windows.Forms.Button creditButton;
private System.Windows.Forms.Button openButton; 28
private System.ComponentModel.Container components = null; 30
// stream through which serializable data are read from file
private FileStream input; 33
// object for deserializing Record in binary format
BinaryFormatter reader = new BinaryFormatter();
CreditInquiry.cs

52. User clicked open button36
// name of file that stores credit, debit and zero balances
private string fileName; 39
[STAThread]
static void Main() {
Application.Run( new CreditInquiryForm() ); } 45
// Visual Studio .NET generated code 47
// invoked when user clicks Open File button
private void openButton_Click(
object sender, System.EventArgs e ) {
// create dialog box enabling user to open file
OpenFileDialog fileChooser = new OpenFileDialog();
DialogResult result = fileChooser.ShowDialog(); 55
// exit event handler if user clicked Cancel
if ( result == DialogResult.Cancel )
return; 59
// get name from user
fileName = fileChooser.FileName; 62
// show error if user specified invalid file
if ( fileName == "" || fileName == null )
MessageBox.Show( "Invalid File Name", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
CreditInquiry.cs
User clicked open button
Instantiate OpenFilelDialog
Show OpenFileDialog

53. Button click event handler
else {
// enable all GUI buttons, except for Open file button
openButton.Enabled = false;
creditButton.Enabled = true;
debitButton.Enabled = true;
zeroButton.Enabled = true; } 75
} // end method openButton_Click 77
// invoked when user clicks credit balances,
// debit balances or zero balances button
private void get_Click( object sender, System.EventArgs e ) {
// convert sender explicitly to object of type button
Button senderButton = ( Button )sender; 84
// get text from clicked Button, which stores account type
string accountType = senderButton.Text; 87
// read and display file information
try {
// close file from previous operation
if ( input != null )
input.Close(); 94
// create FileStream to obtain read access to file
input = new FileStream( fileName, FileMode.Open,
FileAccess.Read ); 98
displayTextBox.Text = "The accounts are:\r\n";
100
CreditInquiry.cs
Button click event handler
Reference to object that sent event
Get text from clicked button
Create read only FileStream for input

54. While loop to read from file
// traverse file until end of file
while ( true ) {
// get next Record available in file
Record record = ( Record )reader.Deserialize( input );
106
// store record's last field in balance
Double balance = record.Balance;
109
// determine whether to display balance
if ( ShouldDisplay( balance, accountType ) ) {
// display record
string output = record.Account + "\t" +
record.FirstName + "\t" + record.LastName +
new string( ' ', 6 ) + "\t";
117
// display balance with correct monetary format
output += String.Format(
"{0:F}", balance ) + "\r\n";
121
// copy output to screen
displayTextBox.Text += output; } } }
127
// handle exception when file cannot be closed
catch( IOException ) {
MessageBox.Show( "Cannot Close File", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); }
134
While loop to read from file
CreditInquiry.cs
Read input from file

55. No more records exception CreditInquiry.cs
// handle exception when no more records
catch( SerializationException ) {
// close FileStream if no Records in file
input.Close(); }
141
} // end method get_Click
143
// determine whether to display given record
private bool ShouldDisplay( double balance, string accountType ) {
if ( balance > 0 ) {
// display credit balances
if ( accountType == "Credit Balances" )
return true; }
153
else if ( balance < 0 ) {
// display debit balances
if ( accountType == "Debit Balances" )
return true; }
160
else // balance == 0 {
// display zero balances
if ( accountType == "Zero Balances" )
return true; }
167
No more records exception
CreditInquiry.cs
Close FileStream
Method to determine whether to display each record in file

56. Done button clicked event handler
return false;
169
} // end method ShouldDisplay
171
// invoked when user clicks Done button
private void doneButton_Click(
object sender, System.EventArgs e ) {
// determine whether file exists
if ( input != null ) {
// close file
try {
input.Close(); }
184
// handle exception if FileStream does not exist
catch( IOException ) {
// notify user of error closing file
MessageBox.Show( "Cannot close file", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error); } }
193
Application.Exit();
195
} // end method doneButton_Click
197
198 } // end class CreditInquiryForm
CreditInquiry.cs
Done button clicked event handler

57. CreditInquiry.cs Program Output

58. CreditInquiry.cs Program Output

59. Allows instant access to information
17.7 Random-Access Files
Allows instant access to information
Individual records can be accessed directly without searching through large numbers of other records
Must be implemented through the application
Easiest when all records are a fixed length
Data can be inserted without destroying other data in file
Records can be updated without rewriting the entire file
Cannot serialize
Won’t guarantee a fixed-length record size

60. 17.7 Random-Access Files 100 200 300 400 500 100 bytes byte offsets
100
200
300
400
500
100 bytes
byte offsets
Fig Random-access file with fixed-length records.

61. Constant to hold record length
1 // Fig : RandomAccessRecord.cs
2 // Data-record class for random-access applications. 3
4 using System; 5
6 public class RandomAccessRecord
7 {
// length of firstName and lastName
private const int CHAR_ARRAY_LENGTH = 15; 10
private const int SIZE_OF_CHAR = 2;
private const int SIZE_OF_INT32 = 4;
private const int SIZE_OF_DOUBLE = 8; 14
// length of record
public const int SIZE = SIZE_OF_INT32 +
* ( SIZE_OF_CHAR * CHAR_ARRAY_LENGTH ) + SIZE_OF_DOUBLE; 18
// record data
private int account;
private char[] firstName = new char[ CHAR_ARRAY_LENGTH ];
private char[] lastName = new char[ CHAR_ARRAY_LENGTH ];
private double balance; 24
// default constructor sets members to default values
public RandomAccessRecord() : this( 0, "", "", 0.0 ) { } 29
RandomAccessRecord.cs
Constant to hold record length
Private members for data storage
Set members to default value

62. Set records to parameter values RandomAccessRecord.cs
// overloaded counstructor sets members to parameter values
public RandomAccessRecord( int accountValue,
string firstNameValue, string lastNameValue,
double balanceValue ) {
Account = accountValue;
FirstName = firstNameValue;
LastName = lastNameValue;
Balance = balanceValue; 39
} // end constructor 41
// property Account
public int Account {
get {
return account; } 49
set {
account = value; } 54
} // end property Account 56
// property FirstName
public string FirstName {
get {
return new string( firstName ); } 64
Set records to parameter values
RandomAccessRecord.cs
Account accessor methods
First name accessor methods

63. Set accessor assures length is only 15 characters{
// determine length of string parameter
int stringSize = value.Length; 69
// firstName string representation
string firstNameString = value; 72
// append spaces to string parameter if too short
if ( CHAR_ARRAY_LENGTH >= stringSize ) {
firstNameString = value +
new string( ' ', CHAR_ARRAY_LENGTH - stringSize ); }
else {
// remove characters from string parameter if too long
firstNameString =
value.Substring( 0, CHAR_ARRAY_LENGTH ); } 85
// convert string parameter to char array
firstName = firstNameString.ToCharArray(); 88
} // end set 90
} // end property FirstName 92
// property LastName
public string LastName {
get {
return new string( lastName ); }
Set accessor assures length is only 15 characters
Get length of string
RandomAccessRecord.cs
Add spaces if length is less then 15 characters
Remove characters if length is more then 15 characters
Last name accessor methods

64. Set accessor assures length of 15 characters
100
set {
// determine length of string parameter
int stringSize = value.Length;
105
// lastName string representation
string lastNameString = value;
108
// append spaces to string parameter if too short
if ( CHAR_ARRAY_LENGTH >= stringSize ) {
lastNameString = value +
new string( ' ', CHAR_ARRAY_LENGTH - stringSize ); }
else {
// remove characters from string parameter if too long
lastNameString =
value.Substring( 0, CHAR_ARRAY_LENGTH ); }
121
// convert string parameter to char array
lastName = lastNameString.ToCharArray();
124
} // end set
126
} // end property LastName
128
Set accessor assures length of 15 characters
Get name length
RandomAccessRecord.cs
Add spaces if length is less then 15 characters
Remove characters if length is more then 15 characters

65. Balance accessor methods RandomAccessRecord.cs
// property Balance
public double Balance {
get {
return balance; }
136
set {
balance = value; }
141
} // end property Balance
143
144 } // end class RandomAccessRecord
Balance accessor methods
RandomAccessRecord.cs

66. 17.8 Creating a Random-Access File
Use class BinaryWriter instead of serialization
By attaching a FileStream to it, bytes can be written directly to a file

67. Save file to disk by invoking method SaveFile
1 // Fig : CreateRandomAccessFile.cs
2 // Creating a random file. 3
4 // C# namespaces
5 using System;
6 using System.IO;
7 using System.Windows.Forms; 8
9 // Deitel namespaces
10 using BankLibrary; 11
12 class CreateRandomAccessFile
13 {
// number of records to write to disk
private const int NUMBER_OF_RECORDS = 100; 16
[STAThread]
static void Main(string[] args) {
// create random file, then save to disk
CreateRandomAccessFile file = new CreateRandomAccessFile();
file.SaveFile(); 23
} // end method Main 25
// write records to disk
private void SaveFile() {
// record for writing to disk
RandomAccessRecord blankRecord = new RandomAccessRecord(); 31
// stream through which serializable data are written to file
FileStream fileOutput = null; 34
CreateRandomAccessFile.cs
Create a random file
Save file to disk by invoking method SaveFile
SaveFile method
Create blank record

68. Instantiate FileStream with user selected file
// stream for writing bytes to file
BinaryWriter binaryOutput = null; 37
// create dialog box enabling user to save file
SaveFileDialog fileChooser = new SaveFileDialog();
DialogResult result = fileChooser.ShowDialog(); 41
// get file name from user
string fileName = fileChooser.FileName; 44
// exit event handler if user clicked Cancel
if ( result == DialogResult.Cancel )
return; 48
// show error if user specified invalid file
if ( fileName == "" || fileName == null )
MessageBox.Show("Invalid File Name", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error);
else {
// write records to file
try {
// create FileStream to hold records
fileOutput = new FileStream( fileName,
FileMode.Create, FileAccess.Write ); 61
// set length of file
fileOutput.SetLength( RandomAccessRecord.SIZE *
NUMBER_OF_RECORDS ); 65
// create object for writing bytes to file
binaryOutput = new BinaryWriter( fileOutput ); 68
Create and display SaveFileDialog so user can specify file name and location
CreateRandomAccessFile.cs
Instantiate FileStream with user selected file
Set length of FileStream to the size of a recod times the number of records
Pass FileStream to BinaryWriter to write bytes directly to file

69. Move file position pointer to next write location
// write empty records to file
for ( int i = 0; i < NUMBER_OF_RECORDS; i++ ) {
// set file position pointer in file
fileOutput.Position = i * RandomAccessRecord.SIZE; 74
// write blank record to file
binaryOutput.Write( blankRecord.Account );
binaryOutput.Write( blankRecord.FirstName );
binaryOutput.Write( blankRecord.LastName );
binaryOutput.Write( blankRecord.Balance ); } 81
// notify user of success
MessageBox.Show("File Created", "Success",
MessageBoxButtons.OK, MessageBoxIcon.Information); } 86
// handle exception if error occurs during writing
catch( IOException ) {
// notify user of error
MessageBox.Show( "Cannot write to file", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); } } 95
Create 100 empty records
CreateRandomAccessFile.cs
Move file position pointer to next write location
Write data to file

70. CreateRandomAccessFile.cs Program Output
// close FileStream
if ( fileOutput == null )
fileOutput.Close(); 99
// close BinaryWriter
if ( binaryOutput == null )
binaryOutput.Close();
103
} // end method SaveFile
105 } // end class CreateRandomAccessFile
Close Filestream
CreateRandomAccessFile.cs Program Output
Close BinaryWriter

71. 17.9 Writing Data Randomly to a Random-Access File

72. WriteRandomAccessFile.cs 1 // Fig 17.16: WriteRandomAccessFile.cs
2 // Write data to a random-access file. 3
4 // C# namespaces
5 using System;
6 using System.Drawing;
7 using System.Collections;
8 using System.ComponentModel;
9 using System.Windows.Forms;
10 using System.Data;
11 using System.IO; 12
13 // Deitel namespaces
14 using BankLibrary; 15
16 public class WriteRandomAccessFileForm : BankUIForm
17 {
private System.Windows.Forms.Button openButton;
private System.Windows.Forms.Button enterButton; 20
private System.ComponentModel.Container components = null; 22
// number of RandomAccessRecords to write to disk
private const int NUMBER_OF_RECORDS = 100; 25
// stream through which data are written to file
private FileStream fileOutput; 28
// stream for writing bytes to file
private BinaryWriter binaryOutput; 31
WriteRandomAccessFile.cs

73. Open Button clicked event handler
[STAThread]
static void Main() {
Application.Run( new WriteRandomAccessFileForm() ); } 37
// Visual Studio .NET generated code 39
// invoked when user clicks Open button
private void openButton_Click(
object sender, System.EventArgs e ) {
// create dialog box enabling user to open file
OpenFileDialog fileChooser = new OpenFileDialog();
DialogResult result = fileChooser.ShowDialog(); 47
// get file name from user
string fileName = fileChooser.FileName; 50
// exit event handler if user clicked Cancel
if ( result == DialogResult.Cancel )
return; 54
// show error if user specified invalid file
if ( fileName == "" || fileName == null )
MessageBox.Show("Invalid File Name", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error);
else {
// open file if file already exists
try {
// create FileStream to hold records
fileOutput = new FileStream( fileName,
FileMode.Open, FileAccess.Write );
WriteRandomAccessFile.cs
Open Button clicked event handler
Instantiate and show OpenFileDialog so user can choose file to write to
Create write only FileStream with user selected file for output

74. Create BinaryWriter to write directly to file67
// create object for writing bytes to file
binaryOutput = new BinaryWriter( fileOutput ); 70
// disable Open button and enable Enter button
openButton.Enabled = false;
enterButton.Enabled = true; } 75
// notify user if file does not exist
catch( IOException ) {
MessageBox.Show("File Does Not Exits", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error); } } 83
} // end method openButton_Click 85
// invoked when user clicks Enter button
private void enterButton_Click(
object sender, System.EventArgs e ) {
// TextBox values string array
string[] values = GetTextBoxValues(); 92
// determine whether TextBox account field is empty
if ( values[ ( int )TextBoxIndices.ACCOUNT ] != "" ) {
// write record to file at appropriate position
try {
// get account number value from TextBox
int accountNumber = Int32.Parse(
values[ ( int )TextBoxIndices.ACCOUNT ] );
Create BinaryWriter to write directly to file
WriteRandomAccessFile.cs
Enter clicked event handler, writes data entered to file
Retrieve data from text boxes

75. Test if accountNumer is valid
102
// determine whether accountNumber is valid
if ( accountNumber > 0 &&
accountNumber <= NUMBER_OF_RECORDS ) {
// move file position pointer
fileOutput.Seek( ( accountNumber - 1 ) *
RandomAccessRecord.SIZE, SeekOrigin.Begin );
110
// write data to file
binaryOutput.Write( accountNumber );
binaryOutput.Write(
values[ ( int )TextBoxIndices.FIRST ] );
binaryOutput.Write(
values[ ( int )TextBoxIndices.LAST ] );
binaryOutput.Write( Double.Parse( values[
( int )TextBoxIndices.BALANCE ] ) ); }
else {
// notify user if invalid account number
MessageBox.Show("Invalid Account Number", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error); } }
127
// handle number-format exception
Test if accountNumer is valid
WriteRandomAccessFile.cs
Move file position pointer
Write data to file using BinaryWriter

76. WriteRandomAccessFile.cs Program Output
catch( FormatException ) {
// notify user if error occurs when formatting numbers
MessageBox.Show("Invalid Balance", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); } }
136
ClearTextBoxes(); // clear text box values
138
} // end method enterButton_Click
140
141 } // end class WriteRandomAccessFileForm
WriteRandomAccessFile.cs Program Output

77. WriteRandomAccessFile.cs Program Output

78. WriteRandomAccessFile.cs Program Output

79. WriteRandomAccessFile.cs Program Output

80. 17.10 Reading Data Sequentially from a Random-Access File
Use class BinaryReader instead of deserialization
By attaching a FileStream to it, bytes can be read directly from a file

81. ReadRandomAccessFile.cs 1 // Fig 17.17: ReadRandomAccessFile.cs
2 // Reads and displays random-access file contents. 3
4 // C# namespaces
5 using System;
6 using System.Drawing;
7 using System.Collections;
8 using System.ComponentModel;
9 using System.Windows.Forms;
10 using System.Data;
11 using System.IO; 12
13 // Deitel namespaces
14 using BankLibrary; 15
16 public class ReadRandomAccessFileForm : BankUIForm
17 {
private System.Windows.Forms.Button openButton;
private System.Windows.Forms.Button nextButton; 20
private System.ComponentModel.Container components = null; 22
// stream through which data are read from file
private FileStream fileInput; 25
// stream for reading bytes from file
private BinaryReader binaryInput; 28
// index of current record to be displayed
private int currentRecordIndex; 31
ReadRandomAccessFile.cs

82. Open Button clicked event handler
[STAThread]
static void Main() {
Application.Run( new ReadRandomAccessFileForm() ); } 37
// Visual Studio .NET generated code 39
// invoked when user clicks Open button
private void openButton_Click(
object sender, System.EventArgs e ) {
// create dialog box enabling user to open file
OpenFileDialog fileChooser = new OpenFileDialog();
DialogResult result = fileChooser.ShowDialog(); 47
// get file name from user
string fileName = fileChooser.FileName; 50
// exit eventhandler if user clicked Cancel
if ( result == DialogResult.Cancel )
return; 54
// show error if user specified invalid file
if ( fileName == "" || fileName == null )
MessageBox.Show( "Invalid File Name", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
else {
// create FileStream to obtain read access to file
fileInput = new FileStream( fileName,
FileMode.Open, FileAccess.Read ); 64
ReadRandomAccessFile.cs
Open Button clicked event handler
Instantiate and show OpenFileDialog so user can choose file to read from
Create FileStream with user selected file

83. Create BinaryReader to read from file ReadRandomAccessFile.cs
// use FileStream for BinaryWriter to read bytes from file
binaryInput = new BinaryReader( fileInput ); 67
openButton.Enabled = false; // disable Open button
nextButton.Enabled = true; // enable Next button 70
currentRecordIndex = 0;
ClearTextBoxes(); } 74
} // end method openButton_Click 76
// invoked when user clicks Next button
private void nextButton_Click(
object sender, System.EventArgs e ) {
// record to store file data
RandomAccessRecord record = new RandomAccessRecord(); 83
// read record and store data in TextBoxes
try {
string[] values; // for storing TextBox values 88
// get next record available in file
while( record.Account == 0 ) {
// set file position pointer to next record in file
fileInput.Seek(
currentRecordIndex * RandomAccessRecord.SIZE, 0 ); 95
currentRecordIndex += 1; 97
Create BinaryReader to read from file
ReadRandomAccessFile.cs
Next button clicked event handler
Instantiate record to store data
Read from file until a nonzero account number is reached
Move file position pointer

84. Use BinaryReader to store file data in record ReadRandomAccessFile.cs
// read data from record
record.Account = binaryInput.ReadInt32();
record.FirstName = binaryInput.ReadString();
record.LastName = binaryInput.ReadString();
record.Balance = binaryInput.ReadDouble(); }
104
// store record values in temporary string array
values = new string[] {
record.Account.ToString(),
record.FirstName,
record.LastName,
record.Balance.ToString() };
111
// copy string array values to TextBox values
SetTextBoxValues( values ); }
115
// handle exception when no records in file
catch( IOException ) {
// close streams if no records in file
fileInput.Close();
binaryInput.Close();
122
openButton.Enabled = true; // enable Open button
nextButton.Enabled = false; // disable Next button
ClearTextBoxes();
126
Use BinaryReader to store file data in record
ReadRandomAccessFile.cs
Display records in TextBoxes
No more records exception handler
Close FileStream and BinaryReader

85. ReadRandomAccessFile.cs Program Output
// notify user if no records in file
MessageBox.Show("No more records in file", "",
MessageBoxButtons.OK, MessageBoxIcon.Information); }
131
} // end method nextButton_Click
133
134 } // end class ReadRandomAccessFileForm
Tell user there are no more records
ReadRandomAccessFile.cs Program Output

86. ReadRandomAccessFile.cs Program Output

87. ReadRandomAccessFile.cs Program Output

88. ReadRandomAccessFile.cs Program Output

89. ReadRandomAccessFile.cs Program Output

90. 17.11 Case Study: A Transaction-Processing Program
Maintains a bank’s account information
Users can add new accounts, update existing accounts and delete accounts
Class Transaction
Acts as a proxy:
Handles all transactions so objects do not have to
Allows abstraction

91. Method to create or open file
1 // Fig : Transaction.cs
2 // Handles record transactions. 3
4 // C# namespaces
5 using System;
6 using System.IO;
7 using System.Windows.Forms; 8
9 // Deitel namespaces
10 using BankLibrary; 11
12 public class Transaction
13 {
// number of records to write to disk
private const int NUMBER_OF_RECORDS = 100; 16
// stream through which data move to and from file
private FileStream file; 19
// stream for reading bytes from file
private BinaryReader binaryInput; 22
// stream for writing bytes to file
private BinaryWriter binaryOutput; 25
// create/open file containing empty records
public void OpenFile( string fileName ) {
// write empty records to file
try {
// create FileStream from new file or existing file
file = new FileStream( fileName, FileMode.OpenOrCreate ); 34
Transaction.cs
Method to create or open file
Create FileStream from new or existing file

92. Create BinaryWriter and BinaryReader from FileStream
// use FileStream for BinaryWriter to read bytes from file
binaryInput = new BinaryReader( file ); 37
// use FileStream for BinaryWriter to write bytes to file
binaryOutput = new BinaryWriter( file ); 40
// determine whether file has just been created
if ( file.Length == 0 ) {
// record to be written to file
RandomAccessRecord blankRecord =
new RandomAccessRecord(); 47
// new record can hold NUMBER_OF_RECORDS records
file.SetLength( RandomAccessRecord.SIZE *
NUMBER_OF_RECORDS ); 51
// write blank records to file
for ( int i = 0; i < NUMBER_OF_RECORDS; i++ ) {
// move file-position pointer to next position
file.Position = i * RandomAccessRecord.SIZE; 57
// write blank record to file
binaryOutput.Write( blankRecord.Account );
binaryOutput.Write( blankRecord.FirstName );
binaryOutput.Write( blankRecord.LastName );
binaryOutput.Write( blankRecord.Balance ); } } } 66
Create BinaryWriter and BinaryReader from FileStream
Transaction.cs
If the file is new, fill it with empty records

93. Get record associated with account number
// notify user of error during writing of blank records
catch( IOException ) {
MessageBox.Show("Cannot create file", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error); } 73
} // end method OpenFile 75
// retrieve record depending on whether account is valid
public RandomAccessRecord GetRecord( string accountValue ) {
// store file data associated with account in record
try {
// record to store file data
RandomAccessRecord record = new RandomAccessRecord(); 84
// get value from TextBox's account field
int accountNumber = Int32.Parse( accountValue ); 87
// if account is invalid, do not read data
if ( accountNumber < 1 ||
accountNumber > NUMBER_OF_RECORDS ) {
// set record's account field with account number
record.Account = accountNumber; } 95
// get data from file if account is valid
else {
// locate position in file where record exists
file.Seek( ( accountNumber - 1 ) *
RandomAccessRecord.SIZE, 0 );
Transaction.cs
Get record associated with account number
Instantiate record to hold data
Find position of record

94. Store file data in record Transaction.cs
102
// read data from record
record.Account = binaryInput.ReadInt32();
record.FirstName = binaryInput.ReadString();
record.LastName = binaryInput.ReadString();
record.Balance = binaryInput.ReadDouble(); }
109
return record; }
112
// notify user of error during reading
catch( IOException ) {
MessageBox.Show( "Cannot read file", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); }
119
return null;
121
} // end method GetRecord;
123
// add record to file at position determined by accountNumber
public bool AddRecord(
RandomAccessRecord record, int accountNumber ) {
// write record to file
try {
// move file position pointer to appropriate position
file.Seek( ( accountNumber - 1 ) *
RandomAccessRecord.SIZE, 0 );
134
Store file data in record
Transaction.cs
Return the record
Method to insert record
Use account number to determine where to enter record

95. If error occurs, notify user
// write data to file
binaryOutput.Write(record.Account);
binaryOutput.Write(record.FirstName);
binaryOutput.Write(record.LastName);
binaryOutput.Write(record.Balance); }
141
// notify user if error occurs during writing
catch( IOException ) {
MessageBox.Show( "Error Writing To File", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
147
return false; // failure }
150
return true; // success
152
} // end method AddRecord
154
155 } // end class Transaction
Write data to file
Transaction.cs
If error occurs, notify user

96. TransactionProcessor.cs 1 // Fig. 17.19: TransactionProcessor.cs
2 // MDI parent for transaction-processor application. 3
4 using System;
5 using System.Drawing;
6 using System.Collections;
7 using System.ComponentModel;
8 using System.Windows.Forms;
9 using System.Data; 10
11 public class TransactionProcessorForm
: System.Windows.Forms.Form
13 {
private System.ComponentModel.Container components = null;
private System.Windows.Forms.MdiClient MdiClient1; 16
// reference to StartDialog
private StartDialogForm startDialog; 19
// constructor
public TransactionProcessorForm() {
// required for Windows Form Designer support
InitializeComponent(); 25
startDialog = new StartDialogForm();
startDialog.MdiParent = this;
startDialog.Show(); } 30
TransactionProcessor.cs

97. TransactionProcessor.cs 31 [STAThread] 32 static void Main() 33 {{
Application.Run( new TransactionProcessorForm() ); } 36
// Visual Studio .NET generated code 38
39 } // end class TransactionProcessorForm
TransactionProcessor.cs

98. StartDialog.cs 1 // Fig. 17.20: StartDialog.cs
2 // Initial dialog box displayed to user. Provides buttons for
3 // creating/opening file and for adding, updating and removing
4 // records from file. 5
6 // C# namespaces
7 using System;
8 using System.Drawing;
9 using System.Collections;
10 using System.ComponentModel;
11 using System.Windows.Forms; 12
13 // Deitel namespaces
14 using BankLibrary; 15
16 public delegate void MyDelegate(); 17
18 public class StartDialogForm : System.Windows.Forms.Form
19 {
private System.Windows.Forms.Button updateButton;
private System.Windows.Forms.Button newButton;
private System.Windows.Forms.Button deleteButton;
private System.Windows.Forms.Button openButton; 24
private System.ComponentModel.Container components = null; 26
// reference to dialog box for adding record
private NewDialogForm newDialog; 29
// reference to dialog box for updating record
private UpdateDialogForm updateDialog; 32
// reference to dialog box for removing record
private DeleteDialogForm deleteDialog; 35
StartDialog.cs

99. Open button clicked method
// reference to object that handles transactions
private Transaction transactionProxy; 38
// Visual Studio .NET generated code 40
// invoked when user clicks New/Open File button
private void openButton_Click(
object sender, System.EventArgs e ) {
// create dialog box enabling user to create or open file
OpenFileDialog fileChooser = new OpenFileDialog();
DialogResult result;
string fileName; 49
// enable user to create file if file does not exist
fileChooser.Title = "Create File / Open File";
fileChooser.CheckFileExists = false; 53
// show dialog box to user
result = fileChooser.ShowDialog(); 56
// exit event handler if user clicked Cancel
if ( result == DialogResult.Cancel )
return; 60
// get file name from user
fileName = fileChooser.FileName; 63
// show error if user specified invalid file
if ( fileName == "" || fileName == null )
MessageBox.Show( "Invalid File Name", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); 68
// open or create file if user specified valid file
StartDialog.cs
Open button clicked method
Create dialog box so user can select file
Show dialog box

100. Instantiate class Transaction object
else {
// create Transaction with specified file
transactionProxy = new Transaction();
transactionProxy.OpenFile( fileName ); 75
// enable GUI buttons except for New/Open File button
newButton.Enabled = true;
updateButton.Enabled = true;
deleteButton.Enabled = true;
openButton.Enabled = false; 81
// instantiate dialog box for creating records
newDialog = new NewDialogForm( transactionProxy,
new MyDelegate( ShowStartDialog ) ); 85
// instantiate dialog box for updating records
updateDialog = new UpdateDialogForm( transactionProxy,
new MyDelegate( ShowStartDialog ) ); 89
// instantiate dialog box for removing records
deleteDialog = new DeleteDialogForm( transactionProxy,
new MyDelegate( ShowStartDialog ) ); 93
// set StartDialog as MdiParent for dialog boxes
newDialog.MdiParent = this.MdiParent;
updateDialog.MdiParent = this.MdiParent;
deleteDialog.MdiParent = this.MdiParent; } 99
} // end method openButton_Click
101
Instantiate class Transaction object
StartDialog.cs
Create or open specified file
Create new, update and delete child menus

101. Method to allow user to create records in the file StartDialog.cs
// invoked when user clicks New Record button
private void newButton_Click(
object sender, System.EventArgs e ) {
Hide(); // hide StartDialog
newDialog.Show(); // show NewDialog
108
} // end method newButton_Click
110
private void updateButton_Click(
object sender, System.EventArgs e ) {
Hide(); // hide StartDialog
updateDialog.Show(); // show UpdateDialog
116
} // end method updateButton_Click
118
private void deleteButton_Click(
object sender, System.EventArgs e ) {
Hide(); // hide StartDialog
deleteDialog.Show(); // show DeleteDialog
124
} // end method deleteButton_Click
126
protected void ShowStartDialog() {
Show(); }
131
132 } // end class StartDialogForm
Method to allow user to create records in the file
StartDialog.cs
Method to allow user to update a record
Method to allow user to delete a record
Displays StartDialog GUI

102. StartDialog.cs Program Output

103. UpdateDialog.cs 1 // Fig. 17.22: UpdateDialog.cs
2 // Enables user to update records in file. 3
4 // C# namespaces
5 using System;
6 using System.Drawing;
7 using System.Collections;
8 using System.ComponentModel;
9 using System.Windows.Forms; 10
11 // Deitel namespaces
12 using BankLibrary; 13
14 public class UpdateDialogForm : BankUIForm
15 {
private System.Windows.Forms.Label transactionLabel;
private System.Windows.Forms.TextBox transactionTextBox; 18
private System.Windows.Forms.Button saveButton;
private System.Windows.Forms.Button cancelButton; 21
private System.ComponentModel.Container components = null; 23
// reference to object that handles transactions
private Transaction transactionProxy; 26
// delegate for method that displays previous window
private MyDelegate showPreviousWindow; 29
UpdateDialog.cs

104. Display record contents
// initialize components and set members to parameter values
public UpdateDialogForm(
Transaction transactionProxyValue,
MyDelegate delegateValue ) {
InitializeComponent();
showPreviousWindow = delegateValue; 37
// instantiate object that handles transactions
transactionProxy = transactionProxyValue; } 41
// Visual Studio .NET generated code 43
// invoked when user enters text in account TextBox
private void accountTextBox_KeyDown(
object sender, System.Windows.Forms.KeyEventArgs e ) {
// determine whether user pressed Enter key
if ( e.KeyCode == Keys.Enter ) {
// retrieve record associated with account from file
RandomAccessRecord record =
transactionProxy.GetRecord( GetTextBoxValues()
[ ( int )TextBoxIndices.ACCOUNT ] ); 55
// return if record does not exist
if ( record == null )
return; 59
UpdateDialog.cs
Display record contents
Retrieve the record

105. If the record is not empty, display its contents in TextBoxes
// determine whether record is empty
if ( record.Account != 0 ) {
// store record values in string array
string[] values = {
record.Account.ToString(),
record.FirstName.ToString(),
record.LastName.ToString(),
record.Balance.ToString() }; 69
// copy string array value to TextBox values
SetTextBoxValues( values );
transactionTextBox.Text = "[Charge or Payment]"; 73 }
else {
// notify user if record does not exist
MessageBox.Show(
"Record Does Not Exist", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); } } 83
} // end method accountTextBox_KeyDown 85
// invoked when user enters text in transaction TextBox
private void transactionTextBox_KeyDown(
object sender, System.Windows.Forms.KeyEventArgs e ) {
// determine whether user pressed Enter key
if ( e.KeyCode == Keys.Enter ) {
UpdateDialog.cs
If the record is not empty, display its contents in TextBoxes
Add user-specified transaction to balance

106. 93 // calculate balance using transaction TextBox value
try {
// retrieve record associated with account from file
RandomAccessRecord record =
transactionProxy.GetRecord( GetTextBoxValues()
[ ( int )TextBoxIndices.ACCOUNT ] );
100
// get transaction TextBox value
double transactionValue =
Double.Parse( transactionTextBox.Text );
104
// calculate new balance (old balance + transaction)
double newBalance =
record.Balance + transactionValue;
108
// store record values in string array
string[] values = {
record.Account.ToString(),
record.FirstName.ToString(),
record.LastName.ToString(),
newBalance.ToString() };
115
// copy string array value to TextBox values
SetTextBoxValues( values );
118
// clear transaction TextBox
transactionTextBox.Text = ""; }
122
UpdateDialog.cs

107. Method to save changes the user made
// notify user if error occurs in parameter mismatch
catch( FormatException ) {
MessageBox.Show(
"Invalid Transaction", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); } }
131
} // end method transactionTextBox_KeyDown
133
// invoked when user clicks Save button
private void saveButton_Click(
object sender, System.EventArgs e ) {
RandomAccessRecord record =
transactionProxy.GetRecord( GetTextBoxValues()
[ ( int )TextBoxIndices.ACCOUNT ] );
141
// if record exists, update in file
if ( record != null )
UpdateRecord( record );
145
Hide();
ClearTextBoxes();
showPreviousWindow();
149
} // end method saveButton_Click
151
UpdateDialog.cs
Method to save changes the user made

108. Method to update the record
// invoked when user clicks Cancel button
private void cancelButton_Click(
object sender, System.EventArgs e ) {
Hide();
ClearTextBoxes();
showPreviousWindow();
159
} // end method cancelButton_Click
161
// update record in file at position specified by accountNumber
public void UpdateRecord( RandomAccessRecord record ) {
// store TextBox values in record and write record to file
try {
int accountNumber = record.Account;
string[] values = GetTextBoxValues();
170
// store values in record
record.Account = accountNumber;
record.FirstName =
values[ ( int )TextBoxIndices.FIRST ];
record.LastName =
values[ ( int )TextBoxIndices.LAST ];
record.Balance =
Double.Parse(
values[ ( int )TextBoxIndices.BALANCE ] );
180
// add record to file
if ( transactionProxy.AddRecord(
record, accountNumber ) == false )
184
return; // if error }
UpdateDialog.cs
Method to update the record
Add record to file

109. UpdateDialog.cs Program Output
187
// notify user if error occurs in parameter mismatch
catch( FormatException ) {
MessageBox.Show( "Invalid Balance", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
193
return; }
196
MessageBox.Show( "Record Updated", "Success",
MessageBoxButtons.OK,
MessageBoxIcon.Information );
200
} // end method UpdateRecord
202
203 } // end class UpdateDialogForm
UpdateDialog.cs Program Output

110. UpdateDialog.cs Program Output

111. NewDialog.cs 1 // Fig. 17.21: NewDialog.cs
2 // Enables user to insert new record into file. 3
4 // C# namespaces
5 using System;
6 using System.Drawing;
7 using System.Collections;
8 using System.ComponentModel;
9 using System.Windows.Forms; 10
11 // Deitel namespaces
12 using BankLibrary; 13
14 public class NewDialogForm : BankUIForm
15 {
private System.Windows.Forms.Button saveButton;
private System.Windows.Forms.Button cancelButton; 18
private System.ComponentModel.Container components = null; 20
// reference to object that handles transactions
private Transaction transactionProxy; 23
// delegate for method that displays previous window
public MyDelegate showPreviousWindow; 26
// constructor
public NewDialogForm( Transaction transactionProxyValue,
MyDelegate delegateValue ) {
InitializeComponent();
showPreviousWindow = delegateValue; 33
NewDialog.cs

112. Method to write record to disk
// instantiate object that handles transactions
transactionProxy = transactionProxyValue; } 37
// Visual Studio .NET generated code 39
// invoked when user clicks Cancel button
private void cancelButton_Click(
object sender, System.EventArgs e ) {
Hide();
ClearTextBoxes();
showPreviousWindow(); 47
} // end method cancelButton_Click 49
// invoked when user clicks Save As button
private void saveButton_Click(
object sender, System.EventArgs e ) {
RandomAccessRecord record =
transactionProxy.GetRecord( GetTextBoxValues()
[ ( int )TextBoxIndices.ACCOUNT ] ); 57
// if record exists, add it to file
if ( record != null )
InsertRecord( record ); 61
Hide();
ClearTextBoxes();
showPreviousWindow(); 65
} // end method saveButton_Click 67
NewDialog.cs
Method to write record to disk
Get empty record
Call method to insert record

113. Method to insert record into file
// insert record in file at position specified by accountNumber
private void InsertRecord( RandomAccessRecord record ) {
//store TextBox values in string array
string[] textBoxValues = GetTextBoxValues(); 73
// store TextBox account field
int accountNumber = Int32.Parse(
textBoxValues[ ( int )TextBoxIndices.ACCOUNT ] ); 77
// notify user and return if record account is not empty
if ( record.Account != 0 ) {
MessageBox.Show(
"Record Already Exists or Invalid Number", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error); 84
return; } 87
// store values in record
record.Account = accountNumber;
record.FirstName =
textBoxValues[ ( int )TextBoxIndices.FIRST];
record.LastName =
textBoxValues[ ( int )TextBoxIndices.LAST];
record.Balance = Double.Parse(
textBoxValues[ ( int )TextBoxIndices.BALANCE ] ); 96
// add record to file
try {
if ( transactionProxy.AddRecord(
record, accountNumber ) == false )
Method to insert record into file
NewDialog.cs
If the record already exists, tell the user
If location is empty, add the record

114. NewDialog.cs Program Output
102
return; // if error }
105
// notify user if error occurs in parameter mismatch
catch( FormatException ) {
MessageBox.Show( "Invalid Balance", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); }
112
MessageBox.Show( "Record Created", "Success",
MessageBoxButtons.OK, MessageBoxIcon.Information );
115
} // end method InsertRecord
117
118 } // end class NewDialogForm
NewDialog.cs Program Output

115. NewDialog.cs Program Output

116. DeleteDialog.cs 1 // Fig. 17.23: DeleteDialog.cs
2 // Enables user to delete records in file. 3
4 // C# namespaces
5 using System;
6 using System.Drawing;
7 using System.Collections;
8 using System.ComponentModel;
9 using System.Windows.Forms; 10
11 // Deitel namespaces
12 using BankLibrary; 13
14 public class DeleteDialogForm : System.Windows.Forms.Form
15 {
private System.Windows.Forms.Label accountLabel;
private System.Windows.Forms.TextBox accountTextBox; 18
private System.Windows.Forms.Button deleteButton;
private System.Windows.Forms.Button cancelButton; 21
private System.ComponentModel.Container components = null; 23
// reference to object that handles transactions
private Transaction transactionProxy; 26
// delegate for method that displays previous window
private MyDelegate showPreviousWindow; 29
// initialize components and set members to parameter values
public DeleteDialogForm( Transaction transactionProxyValue,
MyDelegate delegateValue) {
InitializeComponent();
showPreviousWindow = delegateValue;
DeleteDialog.cs

117. Method to delete a record36
// instantiate object that handles transactions
transactionProxy = transactionProxyValue; } 40
// Visual Studio .NET generated code 42
// invoked when user clicks Delete Record button
private void deleteButton_Click(
object sender, System.EventArgs e) {
RandomAccessRecord record =
transactionProxy.GetRecord( accountTextBox.Text ); 49
// if record exists, delete it in file
if ( record != null )
DeleteRecord( record ); 53
this.Hide();
showPreviousWindow(); 56
} // end method deleteButton_Click 58
// invoked when user clicks Cancel button
private void cancelButton_Click(
object sender, System.EventArgs e) {
this.Hide();
showPreviousWindow(); 65
} // end method cancelButton_Click 67
DeleteDialog.cs
Method to delete a record

118. Method to delete record
// delete record in file at position specified by accountNumber
public void DeleteRecord( RandomAccessRecord record ) {
int accountNumber = record.Account; 72
// display error message if record does not exist
if ( record.Account == 0 ) {
MessageBox.Show( "Record Does Not Exist", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
accountTextBox.Clear(); 79
return; } 82
// create blank record
record = new RandomAccessRecord(); 85
// write over file record with empty record
if ( transactionProxy.AddRecord(
record, accountNumber ) == true ) 89
// notify user of successful deletion
MessageBox.Show( "Record Deleted", "Success",
MessageBoxButtons.OK, MessageBoxIcon.Information );
Method to delete record
DeleteDialog.cs
Test if record exists
If record exists, create an empty one and overwrite existing one

119. DeleteDialog.cs Program Output
else 94
// notify user of failure
MessageBox.Show(
"Record could not be deleted", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); 99
accountTextBox.Clear();
101
} // end method DeleteRecord
103
104 } // end class DeleteDialogForm
DeleteDialog.cs Program Output